Introduction - New Synthetic Routes to Polyoxometalate Containing Ionic Liquids - page 7

sophisticated analytic methods than were available in the 19 th century. Only with X-ray
diffraction, discovered by Max von Laue in 1912 [25] and pioneered by W. H. Bragg and
his son W. L. Bragg [26] , it was possible to gain clarity of the structure. It was the chemist
J. F. Keggin who experimentally solved the D -isomer structure in 1933 and thus lent his
name to this class of cluster-compounds: the Keggin-clusters. [27] Nowadays a broad
structural diversity of clusters is known beside the Keggin cluster (see. Figure 6).
Figure 6 Polyhedral illustrations for some polyoxometalates showing their structural diversity. a) Keggin
structur [XM 12 O 40 ] n- ; b) Dawson structure [X 2 M 18 O 62 ] n− ; c)Lindqvist hexamolybdate [Mo 6 O 19 ] 2- ;
d) Anderson structure [XM 6 O 24 ] n− . Color scheme: addenda atoms M = e. g. Mo VI , W VI , V V : blue, templating
metal X = e.g. B, Si, P: orange, O red.
POMs may also include a variety of heteroatoms ranging from main-group metals (e.g. X
= P, As, Si, Ge) to d-elements (e.g. Cu, Fe, Ni, Mn, Cr) and even lanthanides (e.g. Ce, La,
Sm), turning POMs into one of the structural most diverse inorganic compound class.
They exhibit an almost unmatched range of physical and chemical properties with a rich
chemistry, structural diversity and the ability to form systems ranging in size from the
nano- to the micrometer scale. [28] For this reason POMs have attracted growing interest
to the scientific community during the last few decades with relevance to analytical